**5. Mechanical properties**

There are several aspects that play a major role on the resulting mechanical properties of the composites materials such as adhesion, the size of the filler, the extent of dispersion. The adhesion and dispersion could also be dependent on the processing technique, the polarity and the surface modification applied on the fillers [14].

Slavutsky and Bertuzzi [41] prepared starch reinforced with sugar bagasse nanocrystals (CNCs) through solution casting. The strong interaction between starch and CNCs due to their chemical structure (polarity) similarity resulted in improved mechanical properties. This was promoted by hydrogen bonding resulting from hydroxyl groups on the surface of CNCs interacting with polymer chains which lead to an increase in Young's modulus (from 112 to 520 MPa) and tensile strength (from ~2.8 to ~17.4 MPa). The chemical treatment on either the CNCs or polymer matrix can also be used to improve the mechanical properties of the ensuing nanocomposites [42]. This is as a result of the crosslinking networks of the polymer which additional strength to the stiffer CNCs or the improvement of the interaction/adhesion between the polymer and the CNCs.

The modification of sugarcane bagasse cellulose with zirconium oxychloride was found to improve the interfacial interaction as well as dispersion which resulted in enhanced mechanical properties [17]. The composites were prepared by melt extrusion with high density polyethylene (HDPE) as polymeric matrix, and the Young's modulus and tensile strength increase respectively from 732 to 1233 MPa and 1.54 to 18.2 MPa. Such increment shows that the mechanical properties the high reinforcing effect of these SB-based fillers can be exploited if the suitable modification is applied. It was reported elsewhere that even the pre-treatment of the sugarcane bagasse fiber with strong acid followed by alkali can improve the interaction between the hydrophobic polymer (polypropylene in this case) and the inherently hydrophilic SB [38]. An increase of 16% in tensile strength and 51% in tensile modulus when compared to pure polymer was obtained.

Most of the SB polymer composites are prepared through melt compounding, thus is often based on the hydrophobic thermoplastics. This results in reduction of the mechanical properties of the resulting composite materials due to lack of adhesion as well as inhomogeneous fiber distribution [36, 37]. Chemical treatment can be utilized to improve the distribution as well as interaction/ adhesion between highly hydrophilic SB fibers and hydrophobic thermoplastics [37]. Similarly, the sugarcane bagasse ashes (SBA)-based composites are prepared *via* melt mixing with an additional treatment being applied on either polymeric matrix or ashes to improve the mechanical properties [1, 46]. Since silica has been used as reinforcement of rubbers, the high content of silica in the SBA opens their applicability in rubber composites. Dos Santos et al. [47] reinforced natural rubber with SBA and found that the strong interfacial interaction between the SBA and rubber improved the mechanical properties. A recent study based on the comparison between the commercial silica and SBA reported that it is possible to replace the commercial silica with SBA as rubber reinforcing filler [48]. It was found that the replacement of commercial silica with SBA did not influence the mechanical properties of the composite materials that much.

*4.1.4. Other processing methods*

232 Sugarcane - Technology and Research

**5. Mechanical properties**

Thermosets polymer composites are usually prepared by curing at a temperature depending on the resin-type. The casting of the constituent of the composites onto the steel mold followed by compression molding under certain conditions (pressure, time and/or temperature) influence the properties of the resulting composite material [43–45]. de Sousa et al. [43] studied the effect of pressure on the pre-treated chopped SB-polyester composites. They reported that the combination of all other parameters such as size of the filler, pre-treatment and pressure exerted during molding can be optimized to obtain the desired properties. It is interesting to note that the thermosets have an edge over other polymers due to the fact that it can offer high filler loadings (>65–80 wt%). In addition, the processing temperature is lower when compared to melt mixing and the easy processability. The disadvantage of these composites is that they are not recyclable, and the highly possible alternative is to use them as polymeric fillers or for heat generation. Nevertheless, there has been paradigm shift from synthetic polyesters to a

There are several aspects that play a major role on the resulting mechanical properties of the composites materials such as adhesion, the size of the filler, the extent of dispersion. The adhesion and dispersion could also be dependent on the processing technique, the polarity

Slavutsky and Bertuzzi [41] prepared starch reinforced with sugar bagasse nanocrystals (CNCs) through solution casting. The strong interaction between starch and CNCs due to their chemical structure (polarity) similarity resulted in improved mechanical properties. This was promoted by hydrogen bonding resulting from hydroxyl groups on the surface of CNCs interacting with polymer chains which lead to an increase in Young's modulus (from 112 to 520 MPa) and tensile strength (from ~2.8 to ~17.4 MPa). The chemical treatment on either the CNCs or polymer matrix can also be used to improve the mechanical properties of the ensuing nanocomposites [42]. This is as a result of the crosslinking networks of the polymer which additional strength to the stiffer CNCs or the improvement of the interaction/adhesion between the polymer and the CNCs.

The modification of sugarcane bagasse cellulose with zirconium oxychloride was found to improve the interfacial interaction as well as dispersion which resulted in enhanced mechanical properties [17]. The composites were prepared by melt extrusion with high density polyethylene (HDPE) as polymeric matrix, and the Young's modulus and tensile strength increase respectively from 732 to 1233 MPa and 1.54 to 18.2 MPa. Such increment shows that the mechanical properties the high reinforcing effect of these SB-based fillers can be exploited if the suitable modification is applied. It was reported elsewhere that even the pre-treatment of the sugarcane bagasse fiber with strong acid followed by alkali can improve the interaction between the hydrophobic polymer (polypropylene in this case) and the inherently hydrophilic SB [38]. An increase of 16% in tensile strength and 51% in tensile modulus when compared to pure polymer was obtained.

new class of biodegradable resins to overcome the recycling issues [45].

and the surface modification applied on the fillers [14].

The effect of NaOH treatment on the SB for the polyester composites was found to be improving the adhesion between the composites' components [45]. The alkali treatment led to finer fibers due to dissolution of the hemicellulose which increased the aspect ratio. A maximum improvement with only 1% NaOH was obtained with 13% in tensile strength, 14% in flexural strength and 13% in impact strength compared to untreated composites. This resulted in better interfacial adhesion between the polyester and NaOH-treated fibers. Other surface treatment of the SB fibers utilized as reinforcement of the thermosets were also studied to improve the interfacial adhesion between the fibers and the polymeric matrix [32, 49]. Despite the general observation of the mechanical properties which increases linearly with increase in fiber content some of these treatment significantly improves the overall performance of the thermosets composites [32, 49]. Vilay et al. [49] pre-treated the SB fibers with NaOH followed by acrylic acid (AA). They reported that the AA treatment improved the tensile strength, Young' modulus, flexural strength, and flexural modulus of the composites when compared to the untreated and NaOH-treated fibers. The elastic modulus was also increased for the treated fibers compared to other with glass transition (T<sup>g</sup> ) shifting to higher temperatures. This could be due to the enhanced interfacial adhesion between the polymer and the filler as confirmed by increase in Tg justify the restriction of polymer chains movement by the reinforcing filler.

A rind and pith component of the SB-based unsaturated polyesters composites was investigated [50]. The flexural strength and flexural modulus were found to increase with fiber content for pith and rind fibers; and impact strength showed similar behavior. The tensile properties were also increased as compared to the unfilled polymeric material. It was, however, found that the rind outperform pith based composites. This was related to the structural difference between the pith and rind. The pith consists of big hollow cavities called lumen reducing bulk density of the fiber and acts as acoustic and thermal insulators. On the other hand, the rind have small size lumens and many finer cellulose fibers. Similar study was conducted elsewhere using poly (vinyl chloride) as matrix [11]. It was also reported that the rind/ PVC displayed superior properties (i.e., flexural strength and modulus) when compared to the pith/PVC composites.

impact force was higher for uncarbonized bagasse as compared to carbonized bagasse which was related to the presence of high content of silica adding to the brittleness of the carbonized

Sugarcane Bagasse and Cellulose Polymer Composites http://dx.doi.org/10.5772/intechopen.71497 235

Water absorption is the most important aspect considering the usage of the fiber polymer composite material in various applications with different environmental conditions. Natural fibers are hydrophilic which lead to their mechanical failure during an application. For example, for a sandwich fiber polymer composites delamination between fiber part and a polymer could ensue as a result of moisture absorption. This is directly dependent on the polymer-type, temperature, humidity, fiber loading, orientation, fiber-matrix adhesion, and permeability of the fibers [35, 50, 51]. On the other hand, surface modification of the fibers may improve the interfacial adhesion between the fibers and the polymer matrix which in turn enhance water absorption resistance. This apparently emanated from the hydrophobicity of the fillers and interaction with the hydroxyl groups on the surface of the fillers, thus decreasing the overall water absorption of the composites. Vilay et al. [49] reported that the treatment of the fibers with acrylic acid (AA) improves the water absorption resistance of the composites. The chemical treatment reportedly reduced the hydroxyl groups which improved adhesion between the fibers and polymeric matrix. The difference between the pith and rind on the water absorption was studied by Lee and Mariatti [50]. The bigger size of lumens in the pith-fibers facilitated the water absorption into the composite material when compared to the rind-based composites.

There are two widely used techniques to study the thermal behavior of the natural fiber composites *viz.* thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The TGA is usually used to evaluate both the thermal stability as well as the percentage of the fibers in the composites. The thermal stability of the SB-based fillers were studied by several authors to evaluate the effect of the extraction processes and surface modification [15, 16, 52]. The degradation steps of the fillers give an idea of the resulting product after extraction process. Similarly, the endotherms from DSC often shows the steps involves during heating pro-

Surface modification of the fibers can also change their thermal degradation behavior [32]. In the case of furfural as surface modification, it interacts mainly with lignin components (i.e., phenolic syringyl and guaiacyl) which alter the thermal degradation behavior of the fibers especially the step associated with lignin [32]. The alkali treatment improve the thermal stability of the fibers due to the removal of thermally unstable constituents of the fibers (i.e., hemicellulose, and wax). On the other hand the acid hydrolysis during the extraction of cellulose fibers (MFC) or cellulose nanocrystals (CNCs) introduces some thermally labile groups

cess such as evaporation of water or moisture below 100°C.

reinforced composites (**Figure 2d**).

**6. Water absorption**

**7. Thermal properties**

**Figure 2.** Variation of (a) hardness, (b) tensile modulus, (c) tensile strength, and (d) impact energy with wt% bagasse particles [14].

Agunsoye and Aigbodion [14] compared the mechanical properties of the uncarbonized and carbonized bagasse. The hardness was found to increase with an increase in fiber content due to the brittleness of bagasse particles; however the higher values for carbonized particles were associated with their larger surface area (**Figure 2a**). Similar observations were reported for tensile modulus due to the introduction of stiffer bagasse as compared to the polymeric matrix (**Figure 2b**). They observed an increase in tensile strength up to 30 wt% which was attributed to good distribution and dispersion resulting in strong interaction (**Figure 2c**). Above 30 wt%, the decrease was attributed to the physical interaction and immobilization of the polymer matrix by the presence of mechanical restraints. In addition, the decrease in interfacial area with an increase in particles content contributed to reducing the strength. On the other hand the impact strength results showed that the incorporation of these particles reduced the ability of the matrix to absorb energy and thereby reducing toughness. The ability to resist the impact force was higher for uncarbonized bagasse as compared to carbonized bagasse which was related to the presence of high content of silica adding to the brittleness of the carbonized reinforced composites (**Figure 2d**).
